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Christie Wilcox holding a freshly-caught Physalia physalis. (credit: Rachel Skubel)

In recent decades, trusted first aid resources have recommended stings from man o’ war (Physalia species) be treated differently from other jellies. But when researchers at the University of Hawaiʻi at Mānoa dug into the scientific literature, they found scant evidence to support such individualized first aid.

Adding to a recent push for evidence-based sting treatments, members of the Pacific Cnidaria Research Laboratory (PCRL) at UH Mānoa—Christie Wilcox, lead author of the paper and postdoctoral fellow and Angel Yanagihara, senior author, head of the PCRL and assistant research professor at the UH Mānoa Pacific Biosciences Research Center and John A. Burns School of Medicine—teamed up with colleagues in Ireland to investigate which commonly recommended first aid actions (such as rinsing with seawater) are the most effective for Physalia stings.

The results, published this week in the journal Toxins, defy the recent abandonment of historic advice, and suggest that man o’ war stings are no different than other jellyfish stings; the best first aid is to rinse with vinegar to remove any residual stingers or bits of tentacle left on the skin and then immerse in 45°C (113°F) hot water or apply a hot pack for 45 minutes.

Physalia (Physalia utriculus, also called bluebottles in the Pacific or Physalia physalis, Portuguese man o’ war in the Atlantic) are among the most recognizable stinging jellies with their bright blue tentacles and colorful inflated floating sails. Strandings of bluebottles are common in Hawaiʻi as the onshore winds push thousands of these small, painful critters onto the beaches. Similar mass strandings are frequent with the Atlantic species too, and have been known to cause hundreds of stings in a single day on beaches from Florida to France.

Atlantic man o’ war treatment parallel

Yanagihara teamed up with Tom Doyle, a jellyfish scientist and lecturer with the National University of Ireland Galway. Doyle and his team performed experiments using the Atlantic man o’ war in parallel with those conducted by Wilcox and Yanagihara in Hawaiʻi. The results from opposite sides of the world lined up beautifully: the venom delivered by a man o’ war sting was lessened if the sting site was rinsed with vinegar, regardless of which species of Physalia was used.

Even better, if you have it available, was Sting No More® Spray, a combined stinging capsule and venom-inhibiting product developed by Yanagihara with Department of Defense funding. Seawater rinsing, on the other hand, spread stinging capsules over more area and thus made stings, much worse. To treat stings after rinsing away the tentacles, both groups found 45 minutes of 45°C (113°F) heat application effectively inactivated already-injected venom, while the application of ice packs made stings worse.

For more information, read the news release on the School of Ocean and Earth Science and Technology website.

This Post Has 5 Comments
  1. I have been stung by Portuguese man o war and recently sea lice. In both cases, taking a hot shower inflamed the area and make the sting much worse. i don’t understand your advice to use hot water on the area as that was the worst thing I did. After being stung I was able to function and feel fine until I got home and took a hot shower. The results (and I have pictures) lasted for 2 weeks; itchy and painful. Taking a Benedril was very helpful
    Dottie Sunio

  2. Aloha Dottie,

    Thank you for your comment.

    To be clear, the data indicate that sting outcomes are improved by a 2 step approach. Firstly, the site must be fully rinsed with vinegar (or newer technologies such as StingNoMore spray that contain vinegar as well as urea and other actives). Without the first step any residual undischarged stinging capsules (of which there are thousands) can and will fire off later. These stinging capsules are microscopic and like ticking time bombs. Fresh water or pressure ( rubbing, scraping) will cause them to fire. If your man o war and sea lice contact areas had not been first rinsed with vinegar, then the first moments of fresh water in the shower will cause them to fire. Hot water immersion is a recommended first aid AFTER vinegar flooding. That said, the data show that een without vinegar as a first step, immersion for at least 20 minutes but best for 45 minutes in hot water (45oC ~114oF) irreversibly inhibits the venom. Unfortunately, showering involves fresh water and site pressure that can trigger competent stinging cells to fire. The shower exposure to heat is not as efficient as immersion (bath) and usually shorter; showers do not allow continuous heating of the tissue. All that said, optimal inhibition of venom and best outcomes were observed after StingNoMore Spray followed by StingNoMore Cream treatment which does not require shower or hot water immersion as the second step of first aid.
    To recap, data show that effective first aid involves both 1) Vinegar rinse followed by 2) 45 min immersion in 45oC (~115oF safe hot water) . Better is 1) StingNoMore Spray followed by 2) StingNoMore Cream.

    In your case summary, the sting “got worse” in the shower. The fact that the skin appeared more inflamed suggests that there were many stinging cells left on your skin that discharged upon showering. We also find this in the experimental models when we briefly spray a sting site with tepid/warm water. Your report that topical Benadryl (diphenhydramine) worked to manage the inflammation is also in keeping with our findings ((diphenhydramine is one of the secondary components of the StingNoMore cream).

    Best regards,
    Angel Yanagihara

  3. Do the results apply to box jellyfish stings? I heard the treatment between man o’ war and box jelly’s are different.

    Mahalo for your research!


  4. What would you do in a situation where you don’t have the recommended products? Sounds like one should rinse it, which means we leave the stingers as is and deal with the pain.

    Also, on a recent Hawaiian Airlines flight, I swear I read that the hawaiian practice for the jellyfish sting was to crush naupaka leaves and put it on the stung area.

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